The present invention relates to seals in a gas turbine for supplementing the chordal hinge seals between turbine nozzles and a turbine nozzle support ring and particularly relates to supplementary seals for substantially minimizing or eliminating leakage losses past the chordal hinge seals.
In a gas turbine, hot gases of combustion flow from combustors through first-stage nozzles and buckets and through the nozzles and buckets of follow-on turbine stages. The first-stage nozzles typically include an annular array or assemblage of cast nozzle segments each containing one or more nozzle stator vanes per segment. Each first-stage nozzle segment also includes inner and outer band portions spaced radially from one another. Upon assembly of the nozzle segments, the stator vanes are circumferentially spaced from one another to form an annular array thereof between annular inner and outer bands. A nozzle retaining ring coupled to the outer band of the first-stage nozzles supports the first-stage nozzles in the gas flow path of the turbine. An annular nozzle support ring, preferably split at a horizontal midline, is engaged by the inner band and supports the first-stage nozzles against axial movement.
In an exemplary arrangement, eighteen cast segments are provided with two vanes per segment. The annular array of segments are sealed one to the other along adjoining circumferential edges by side seals. The side seals seal between a high pressure region radially inwardly of the inner band, i.e., compressor discharge air at high pressure, and the hot gases of combustion in the hot gas flow path which are at a lower pressure.
Chordal hinge seals are used to seal between the inner band of the first-stage nozzles and an axially facing surface of the nozzle support ring. Each chordal hinge seal includes an axial projection which extends linearly along a chord line of the inner band portion of each nozzle segment. Particularly, the chordal hinge seal extends along an inner rail of each segment and which rail extends radially inwardly of the inner band portion. The chordal hinge seal projection lies in sealing engagement with the axially opposite facing sealing surface of the nozzle support ring.
During operation and/or repair of the first-stage nozzle, it has been found that warpage can leave gaps between the chordal hinge seals and the sealing surface of the nozzle support ring. These gaps enable leakage past the chordal hinge seals from the high pressure area radially within the annular inner band into the hot gas flow path. That is, the chordal hinge seals are inadequate to prevent leakage flow as the chordal hinge seal projections lose contact with the sealing surface of the nozzle support ring. Consequently, there is a need for a supplemental seal at the interface of the first-stage nozzles and nozzle support ring to minimize or eliminate the leakage flow past the chordal hinge seals.
In accordance with a preferred embodiment of the present invention, there is provided a supplemental seal between the first-stage nozzles and the nozzle support ring which eliminates or minimizes leakage past the chordal hinge seals. The supplemental seal includes a flexible, preferably sheet metal, leaf seal secured between the inner rail of each nozzle segment and the sealing surface of the nozzle support ring on the high pressure side of the chordal hinge seal. Particularly, the supplemental leaf seal has an arcuate first margin which is received in an arcuate groove opening along the inner face of the inner rail. The first margin is preferably pinned in the groove by a plurality of pins at spaced circumferential positions along the inner rail. The flexible seal extends generally radially inwardly, terminating in an arcuate second margin extending in a generally circumferential direction. A face of the second margin engages a seat projecting axially from the annular surface of the nozzle support ring.
The supplemental leaf seal lies directly between the high pressure region and regions radially outwardly of the supplemental seal, including the chordal hinge seal. Leakage flow past the chordal hinge seal is therefore minimized or eliminated as a result of the sealing of the second margin of the supplemental seal against the seat of the nozzle support ring. The supplemental seals may be overlapped along their end edges to seal the gaps between the nozzle segments. It will be appreciated that upon axial warpage or deformation of the nozzle support ring or nozzle segments, or both, the flexible leaf seal of the supplemental seal is maintained in sealing engagement against the seat by the difference in pressure between the high and low pressure regions on opposite sides of the seal.
In a preferred embodiment according to the present invention, there is provided a turbine comprising a turbine nozzle support ring having a generally axially facing first surface, a turbine nozzle segment having at least one stator vane and including an inner band carrying an inner rail, the inner rail having a second surface in axial opposition to the first surface, one of the first and second surfaces including an axially extending projection therealong for engagement with another of the first and second surfaces to form a first seal therebetween and a supplemental seal extending between the inner rail and the support ring at a location radially inwardly of the first seal and between at least opposite end edges of the segment, the supplemental seal including a seat projecting axially from the support ring and a flexible leaf seal having a first margin thereof secured to the inner rail and a second margin sealingly engageable against the seat.
In a further preferred embodiment according to the present invention, there is provided a gas turbine comprising a turbine nozzle support ring having a generally axially facing first surface, a plurality of turbine nozzle segments each having at least one stator vane and an inner rail, the inner rails of the segments forming a generally annular second surface in axial opposition to the first surface, each of the segments including an axially extending projection along the second surface thereof for engagement with the first surface to form a first seal therebetween, a plurality of supplemental seals extending between the inner rails and the support ring at locations radially inwardly of the first seals, each supplemental seal including a seat projecting axially from the support ring and a flexible leaf seal having a first margin secured to the inner rail, and a second margin sealingly engageable against the seal.